Fix DummyChatProvider interference with health check tests

tests/Tgstation.Server.Tests/Live/DummyChatProvider.cs

@@ -44,6 +44,8 @@ namespace Tgstation.Server.Tests.Live
 
 		ulong channelIdAllocator;
 
+		public static Task MessageGuard = Task.CompletedTask;
+
 		static IAsyncDelayer CreateMockDelayer()
 		{
 			// at time of writing, this is used exclusively for the reconnection interval which works in minutes
@@ -219,6 +221,8 @@ namespace Tgstation.Server.Tests.Live
 					var delay = random.Next(0, 10000);
 					await Task.Delay(delay, cancellationToken);
 
+					await MessageGuard;
+
 					// %5 chance to disconnect randomly
 					if (enableRandomDisconnections != 0 && random.Next(0, 100) > 95)
 						connected = false;

tests/Tgstation.Server.Tests/Live/Instance/WatchdogTest.cs

@@ -165,9 +165,21 @@ namespace Tgstation.Server.Tests.Live.Instance
 			await RunLongRunningTestThenUpdateWithNewDme(cancellationToken);
 			await RunLongRunningTestThenUpdateWithByondVersionSwitch(cancellationToken);
 
+			// no chatty bullshit while we test health checks
+			var tcs = new TaskCompletionSource();
+			var oldTask = Interlocked.Exchange(ref DummyChatProvider.MessageGuard, tcs.Task);
+
 			await RunHealthCheckTest(true, cancellationToken);
 			await RunHealthCheckTest(false, cancellationToken);
 
+			async void Cleanup()
+			{
+				await oldTask;
+				tcs.SetResult();
+			}
+
+			Cleanup();
+
 			await InteropTestsForLongRunningDme(cancellationToken);
 
 			await instanceClient.DreamDaemon.Update(new DreamDaemonRequest